(7/19/13) Preliminary autopsy results show that a two-year-old Polk County boy died from hyper-thermia – a large spike in his body heat – after he was found dead in a car trunk on Wednesday night.

Isaiah Theis (ties) was found in a customer's vehicle while it was waiting for service at an auto repair business run by the boy's father at his home near Centuria. Officials have not said how he got into the trunk – where he was not visible to searchers who passed by the cars several times after Isaiah disappeared Tuesday night. Toxicology test results are pending. Polk County sheriff's officials said early results showed that the toddler was well-nourished and well-developed, and was not sick or had any life-threatening injuries or bone fractures. The exact cause of Isaiah's death remains under investigation. He was stuck in 90-degree heat, while over 24-hundred volunteers were looking for him.